In recent years, more and more subscribers access Internet via mobile terminals. The users' mobile terminals include mobile phones, notebook computers, personal digital assistants, and so on. The booming mobile internet makes mobility an important element in group communication. Group communication includes a variety of applications, such as: content broadcasting and streaming, voice and video conferencing, massive multiplayer gaming, even the distributed systems, traffics or self-organization of autonomous networks. Any Source Multicast (ASM) is very suitable for many-to-many communication. In Mobile Internet, the mobility of multicast source can be is unavoidable.
Existing solutions for the mobility of multicast source can be sorted in three categories:
Statically Rooted Distribution Trees
Romdhani, I. and others proposed using rendezvous point (RP) solving the mobility problem of multicast source in “Transparent handover for mobile multicast source” published in ‘Proceedings of the IEEE ICN’ 06. We call the point as “Mobility-aware Rendezvous Points (MRP)”. The basic idea of the solution is: When a mobile point, which is also a mobile source, moves into a foreign network, the mobile point gets a Care-of-Address (CoA). Before the mobile multicast source sends data to a multicast group, the mobile multicast source has to register to the MRP the binding between its CoA and Home Address (HoA) of the mobile multicast source, as well as other related information, such as: Security Association, and CoA's lifetime etc. Therefore, MRP can know that the CoA identified source is the same multicast source as the HoA identified source, but just moved. Thus when the multicast data package, using CoA as the source IP address, appears, MRP can identify that the data packet is actually sourced from the formerly source identified by HoA. Hence, MRP modifies the source IP of the arrived multicast data package to HoA, and sends the multicast data package following the shared multicast tree which uses MRP as the root point. By this way, the CoA is transparent to members of group multicast group, that is transparent to the receivers of the multicast content, hence avoiding the re-construction of shared multicast tree.
Reconstruction of Distribution Trees
Several authors proposed to construct a completely new distribution tree after the movement of a multicast source, thereby having to compensate the routing delays. In Schmidt, T. C. and Waehlisch, M's “Seamless Multicast Handover in a Hierarchical Mobile IPv6 Environment” and the “Scalable Multicast Protocol in IP-Based Mobile Networks” published by Lin, C. R. and others in Wireless Networks and Applications, 2000, page 259-271, both have involved the above solution.
Tree Modification Schemes
Chang, R.-S. and Yen, Y.-S. proposed in “A Multicast Routing Protocol with Dynamic Tree Adjustment for Mobile IPv6”, in the Distance Vector Multicast Routing Protocol (DVMRP) solution, using Reverse Traffic Interface (RTI), establishing a Backward-Forced Path (BFP) between the new “multicast tree root point” and the original “multicast tree root point”, in order to save the integrity of the original multicast trees, at the same time of avoiding the rebuilding of the multicast trees, still allowing all the recipients to continue to receive the multicast stream. In the same domain, using the way of shared multicast trees can greatly reduce the mobility related complexity. In above three implementing solutions: compared to the other two ways, statically rooted MRP method needs the least change to the existing multicast routing protocol, such as the PIM-SM protocol, and it can work conveniently with PIM-SM (Protocol Independent Multicast-Sparse Mode) and MSDP (Multicast Source Discovery Protocol). Hence, compared to other two solutions, the statically rooted shared trees solution is more easy to be implemented and deployed. Therefore, it can be determined that the solution is the most advantageous implementing way of ASM with multicast source mobility solutions by now.